Sewage Treatment
Generally, municipal sewage plants have treatment systems that use an influent pretreatment unit to remove substantial amounts of non-organic matter and separate waste water. The waste water is then discharged in to a holding well and is optionally used downstream. The remaining sewage matter is transferred to a primary settling tank, in which solids precipitate. Solids collected from the primary settling tanks are pumped to waste solids digesters having bacteria that digest the solids. In one method commonly used, the solids remaining after digestion, including biological matter, are transferred to an unheated digester for settling, which occurs after about 6 to 12 hours. The settled sludge is then pumped to a drying bed, compressed and transferred to an incinerator for heat processing. Incineration requires air scrubbers to remove any potentially hazardous components that may get released into the environment. In some cases, the sludge is pumped to sand drying beds to dry and is then hand shoveled prior to being hauled to incinerators. Sewage matter or sludge remaining after heat treatment is placed in land fills and/or bio-waste dumps.
The steps of removing, processing and transferring sludge from sewage is costly and effects a low handling capacity. These factors are improved if the amount of sludge generated in the sewage treatment process is reduced. Conventional sewage treatment involves the step of digestion with naturally-occurring bacteria, including aerobic and/or anaerobic bacteria. Anaerobic approaches are generally thought to be less expensive and less invasive than aerobic approaches, largely due to the high cost and engineering challenge associated with the subsurface delivery of oxygen for aerobic treatment and the need for large amounts of storage capacity. However, the products of anaerobic digestion present problems such as corrosion and odor. Efforts to improve the removal of waste and xenobiotics, which includes any synthetic compound that is not natural to an environment, such as pesticides, detergents and plastics, are currently being made in the area of bioremediation.
Bioremediation
The “principle of microbial infallibility” (Alexander, 1965) is an expression of the empirical observation that, in favorable environmental conditions, there are no natural organic compounds which are totally resistant to biodegradation. Bioremediation processes exploit this theory by using populations of microorganisms to a clean contaminated site. These processes include bioenhancement, which involves natural populations of microorganisms, and bioaugmentation, which involves specially developed microbial cultures that are commonly propagated by fermentation. The efficacy and success of bioremediation treatment depends upon several factors including the chemical and physical properties of a contaminated matrix and the effectiveness of the microbial culture/s and treatment protocol.
Various microorganisms have been found to detoxify a number of toxic chemical pollutants (see, for example, G. Chaudry, 1984). Biodegradation or detoxification of chemical pollutants is normally the result of one or more enzymatic reactions, including oxidation, reduction, hydrolysis, and conjugation (see, for example, D. W. Connell, & G. J. Miller, 1984). For example, microbes such as Pseudomonas spp., Mycobacterium and Norcardia, are known to consume hydrocarbons by oxic degradation and, thus, are able to degrade active ingredients in herbicides.
A factor limiting the efficacy of prior art bioremediation processes is the tendency of microorganisms to lose viability and decline in number following their introduction to the remediation site. This has been demonstrated with respect to bioremediation of contaminated soil (see, for example, J. D. van Elsas, & C. E. Heijnen, 1990). Factors that work against the propagation and survival of microorganisms include: competition with other organisms for nutrients, water and space; parasitism, antibiosis and predation by other organisms; and unfavorable physicochemical parameters, including sub-optimal pH, water and oxygen concentrations. In the case of polluted sewage systems, problems associated with survival and propagation of microorganisms introduced for bioremediation may be exacerbated by the presence of toxic pollutants at concentrations which are inimical to microbial growth.
Examples in the art directed to systems and methods to overcome these deficiencies have been described. For example, U.S. Pat. No. 6,204,049 to Bennett et al. describes a composition for remediating a polluted medium by degrading chemical pollutants comprising an inoculum of Marasmiellus troyanus, an alginate carrier and a nutrient. U.S. Pat. No. 4,668,512 to Lewis et al. discloses a formulation of fungi with wheat bran to form alginate gel pellets, for the control of soil-borne plant pathogens, wherein the wheat bran provides a nutrient source for the fungus.
In terms of water treatment, several processes directed to denitrification of drinking water have been described (see, for example, Published U.S. application 2002/0020664 to Tartakovsky, et al.). In situ bioremediation of contaminated water using a microbial biofilter is described in U.S. Pat. Nos. 6,165,356 and 6,036,852 to Carman et al. The biofilter is formed in situ and comprises a bacteria cell biomass having a longevity of at least 8 weeks. Carman et al. teach that the bacteria is methanotrophic, such as Methylosinus trichosporium. 
Processes directed to the bioremediation of sewage waste matter have also been described. For example, U.S. Pat. No. 5,811,290 to Varadaraj describes urea-surfactant clathrates and their use in enhancing the microbial degradation of hydrocarbon contaminated soil, water, or sludge. The method comprises applying to the soil, water or sludge a degradation effective amount of a composition consisting essentially of a phosphorous source and at least one urea non-ionic surfactant adduct, wherein the urea and non-ionic surfactant in the adduct are present in a weight ratio ranging from about 98:2 to about 75:25; and wherein the composition has a N:P ratio ranging from about 10:2 to about 10:0.5; and the applying of the composition is carried out to provide in the soil, water, or sludge a C:N:P ratio of about 100: 10:1 to about 100:1:001 based on the weight percent of hydrocarbon contaminate in the soil, water or sludge.
U.S. Pat. No. 6,254,776 to Seagle describes a bioremediation system and method for treating farm animal waste to remove volatile organic compounds (“VOC”) from wastewater treatment pits, and, thus control smell, is disclosed. The farm animals are housed in structures equipped with grated flooring to permit animal waste to fall into pits or reservoirs below. The pits contain water inoculated with a special assemblage of natural microbes to which oxygen is supplied through piping arranged in the pits. These microbes are taught preferably to be a mixture of 18 naturally occurring aerobic microbes to have an affinity for ammonia and to convert much of the animal waste into carbon dioxide, fatty acids, and water. The system also includes a second piping network situated beneath the grated flooring which serves to create a negative air situation by which escaping foul-smelling air is pulled back into the wastewater to permit further action on the VOC by the microbes in the water. This bioremediation process is taught to result in less odor emitted and fewer waste solids to be disposed of, further processed, or placed directly in storage lagoons.
Another consideration in the design of an effective bioremediation system is the lifetime of the microbes in the system. To supply microbes, bacterial culturing systems are known that produce bacteria on site, for example, at a waste treatment plant. However, these systems use elaborate culturing systems. U.S. Pat. No. 6,087,155 to York, et al. teaches an on site bioremediation system that delivers logarithmically growing, active microorganisms from a culture vessel directly to the biodegradable waste to be metabolized. York et al. describe the bioremediation system including a controller, culture vessel and separate containers of stock microorganisms and nutrient medium, and periodic or continuous addition of stock microorganisms and fresh nutrient media is required to obtain a particular cell density. At that density, the active, logarithmically growing microorganisms flow out of the system to the waste site on a periodic or continuous basis. Regardless of the type of matter being subjected to remediation, continuous treatment requirements increase the costs associated with the treatment.
Prior to the present invention, processes directed to reduce the amount of solid matter, sludge and odor in sewage have lacked time- and cost-effectiveness for applications in sewage plants. There accordingly remains a need in the art for inexpensive, simplified systems and methods for the in situ bioremediation of sewage matter, in particularly, remediating sludge, odor-causing matter and illegal contaminants from the sewer. As described herein, the present invention provides these advantages in the field of sewage treatment. More particularly, the present invention provides an in situ bioremediation system that remains effective over long periods of time without requiring post-processing of, or transfer of sludge. Consequently, the present invention provides a system and method that affords increased handling capacity, decreased cost associated with treatment, and increased environmental safety in the treatment of sewage matter.